Regular Expressions - Practice exercises

You can do all the following exercises for a single string.
Source : https://www.w3resource.com/python-exercises/re/

It's done as a string of words to show what type of strings would and would not be matched.
Remove the \b when feeding a single word in a string.

\b : the empty string, but only at the start or end of the word
Specify in raw (r) format to avoid the clash of \ as an escape and \ to give meaning in Python

Note: \b and \B definitions depends on \w and \W 

It is a boundary between a \w and a \W

1. String that has an a followed by zero or more b's

there should be an a followed b 0 or more b's


>>> s = 'a ab abb b ababa'
>>> import re
>>> re.findall(r'\bab*',s)
['a', 'ab', 'abb', 'ab']

2. a string that has an a followed by three 'b'.

you can use the {m} to specify the amount of times the preceding character/special character should be repeated.

>>> s = 'a ab abb b abbbb abbb‘
>>> re.findall(r'\babbb\b',s)
['abbb']
>>> re.findall(r'\bab{3}\b',s)
['abbb']

3. one upper case letter followed by lower case letters

set [] matches a single character within.

Hyphen - between 2 characters specify a range

Hyphen in beginning or end just matches it literally

>>> s= 'Awesome great Wow'

>>> re.findall(r'\b[A-Z][a-z]*\b',s)

['Awesome', 'Wow']

4. string that has an 'a' followed by anything, ending in 'b‘

s='abbbccb bbbaccb ab'

>>> re.findall(r'\ba.*?b\b',s)

['abbbccb', 'ab']

5. matches a word containing 'z‘

\w used to match a word either in the beginning or end or separated by set of whitespace characters

>>> s = 'bizzare zebra running wild‘

>>> re.findall(r'\w*z\w*',s)

['bizzare', 'zebra']

6. matches a word containing 'z', not at the start or end of the word

This demonstrate the use of \B which is the opposite of \b

This matches a string but not at the start or end of a word.

>>> s='zebra‘

>>> re.search(r'\Bz\B',s)  # no match

>>> s='bizzare'

>>> re.search(r'\Bz\B',s)

<re.Match object; span=(2, 3), match='z'>